The invention relates to solar panels of solar collectors and provides a solar panel having a coating of improved efficiency.
Solar collectors have been devised to use solar energy to heat and cool service systems to structures. These systems use solar collectors which heat a fluid flowing through a housing, each solar collector having at least one cooperative, substantially flat, thermally conductive solar panel providing an energy absorbent "black" surface on a metal substrate. The energy absorbent "black" surface is most economically provided as a coating.
Desired properties of the "black" surfaces are ability to adhere to the thermally conductive substrate, corrosion protection of the substrate, maximum absorption of the energy from solar radiation, minimum emissivity of infrared radiation, long range durability under solar radiation and weathering, low cost, and ease of application.
"Black" surfaces presently are either coatings applied to the surface of the substrate or an oxidized substrate surface. An example of the latter is a copper substrate having an oxidized surface. Although the oxidized surface of a copper substrate can be used as an energy absorbing surface, it is relatively expensive. Electrodeposited coatings applied to the surface of the substrate can be of iron, nickel, or chromium. The electrodeposited coatings are also relatively expensive, and have a further disadvantage in that the electrodeposition process is not reliable and proceeds at a low yield. In addition, electrodeposited coatings often deteriorate and the differences between stable and unstable coatings are not presently understood.
Electrodeposited coatings based on iron are lower in cost than electrodeposited coatings of chromium or nickel, but demonstrate a relatively low absorption of incident solar radiation.
Applied coatings based on graphite which are generally in the form of paints are lower in cost. Their major disadvantage is that most of the absorbed solar energy is lost by emittance. Graphite coatings are widely used despite low efficiency because of cost.
It is desirable to provide a low cost adherent coating on the surface of a solar panel, which has an improved spectral selectivity as compared to a coating produced using a graphite paint. "Spectral selectivity" as used in the art and in this application is the ability to absorb a large percentage of incident solar radiation while emitting only a small portion of the absorbed energy as infrared radiation.